Use

Prefer is considerably faster than formalin, and will produce superior results in a conveniently short time. Small biopsies will fix in 45-60 minutes, larger ones in 1-2 hours. General surgical specimens no thicker than 4 mm will fix adequately in 2-4 hours. Allow longer time when fixing gross specimens. Notice the exquisite detail in the gastric biopsy (Figure at left, Gastric biopsy fixed 45 minutes in Prefer). Basement membranes and cell membranes are clearly defined. Nuclear patterns are good.

Prefer's mild acidity accelerates penetration and chemical fixation. For fatty specimens, we recommend that you make an alcoholic version of Prefer from our Prefer Concentrate. This can be used in one or more stations of the tissue processor

Table 1. is a representative list of primary antibodies our customers use without resorting to antigen recovery procedures. You may recognize some examples that prove difficult when tissues are fixed in NBF. Hormone receptors are demonstrated just as easily. Capricious antigen retrieval methods are virtually eliminated with Prefer!

Table 1. Antibodies used without antigen retrieval on Prefer fixed tissues

Mode of action

The active ingredient of Prefer is glyoxal, in a buffered mixture of water and ethanol. The ethanol content is minimal and does not contribute directly to fixative effects. Glyoxal is a di-aldehyde, structured as if two formaldehyde molecules were attached back-to-back (green atoms are oxygen, blue are carbon, yellow are hydrogen). It acts like formaldehyde to a certain extent, creating familiar morphologic patterns of fixation. The similarity stops there, however. Immunoreactivity is fully maintained, just as in the zinc formalin fixatives, so that antigen recovery procedures rarely if ever have to be employed. Tissues become gently firmed but not over-hardened after fixation, making sectioning easier.

Safety

To be effective, no fixative can be totally safe. Prefer is a very effective fixative, and will fix your fingers and corneas just as readily as it will your surgical specimens. Nitrile gloves and goggles are standard personal protective equipment (latex surgical gloves are ineffective against all chemical exposures).

The real issue of safety with formalin is carcinogenicity and inhalation exposure. Neither of these is a factor with Prefer. Glyoxal has such low vapor pressure that it cannot evaporate to any significant degree. Vapor monitoring is not needed, and all of the regulatory problems associated with formalin are nonexistent with glyoxal.

Prefer is ideal for use anywhere, but is particularly nice to have in poorly ventilated areas or non-laboratory settings like clinics and physicians' offices.

Disposal

Drain disposal is the recommended method of disposal, provided approval is granted by local wastewater treatment authorities. Prefer and Prefer Concentrate exhibit a low order of environmental toxicity and a low potential to bioaccumulate. There is no inhibition of bacteria in wastewater effluent when glyoxal is properly introduced into an acclimated biological treatment facility. All ingredients in Prefer consist solely of carbon, hydrogen and oxygen. Prefer is readily biodegradable to carbon dioxide and water.

Glyoxal itself is not an EPA-listed hazardous waste. In the concentration present in these products, it does not possess any characteristics that qualify it as a hazardous waste by the EPA. It is the ethanol and the pH that qualifies Prefer and properly diluted Prefer Concentrate as hazardous waste. Undiluted Prefer Concentrate is not ignitable and qualifies as hazardous only because of its pH.

ANATECH LTD. suggests that waste Prefer, Prefer Concentrate and properly diluted Prefer Concentrate be introduced into the sanitary sewer system slowly, at the rate of 1-5 gallons per hour. To do this, trickle the waste into the sink from a 5 gallon carboy or drum equipped with a spigot which is barely turned on. The normal flow of wastewater through the generator's facility will dilute the waste and render it non-ignitable [flash point > 140 F (60 C)]. However, do not simply add water to the waste; rather, let the normal waste stream from the facility accomplish the dilution. Under this regimen, waste Prefer will have no effect on biological or chemical processes at wastewater treatment plants. Neutralization of the pH should not be necessary in most sewer districts, but in the event that it is, use magnesium oxide or magnesium hydroxide (neither one will make the solution too alkaline).